Brushless ultra-efficient regenerative servomechanism

Abstract

A servomechanism regeneratively controls motion by a brushless coreless axial-field motor, exerting torque thru its permanent-magnet disk rotor, resulting from synchronized polyphase sinusoidal stator currents, controlled by a switching controller responsive to input commands and to Hall-effect transducer signals that vary sinusoidally with rotor angle and respectively correspond to stator phases. The controller operates with a dc power source and sink. Its signal processors derive from the transducer signals instantaneous magnitudes and polarities thereof and continuous lagless speed feedback. The instantaneous magnitudes are multiplied by a torque amplitude signal to provide respective synchronized amplitude control signals. Current transformers having primary windings in series with power switching transistors provide current feedback pulses with amplitude proportional to instaneous current in associated stator windings. Pulse control means initiate bi-phase pulses having restricted duty-cycle, and dictate pulse duration by comparing each current feedback pulse with the associated synchronized amplitude control signal. Switching logic responsive to the bi-phase pulses, to forward and reverse drive and brake commands, and to said polarities, accordingly controls selection and duty-cycle of said power switching transistors which, cooperative with free-wheeling diodes and inductors, effect controlled alternating stator currents. Various signal interface means process the input commands with feedback derived from the transducer signals, such as speed, direction of rotation, and interpolated digital position, to provide said torque amplitude signal, and variously, said drive and brake commands; so the motor and controller constitute a complete servomechanism, that provides precise speed and position control with regenerative reversing and braking, ultra-high efficiency, and fast dynamic response.

Accordingly, I claim: 
     
       1. Cooperative with a polyphase synchronous motor in a servomechanism for providing regenerative motion control, a switching controller, responsive to various input commands and to polyphase transducer signals that vary sinusoidally with rotor angle and correspond to respective stator phases, for synchronously controlling polyphase stator current; including in combination: means for deriving, from the transducer signals, the instantaneous magnitudes, polarities, and frequency thereof;   signal interface means, responsive to various input command signals, and variously, to the instantaneous magnitudes, polarities, and frequency, for providing a torque amplitude signal, and variously, binary forward drive, reverse drive, and brake commands;   multiplier means, responsive to the instantaneous magnitudes and to the torque amplitude signal, for providing respective synchronized amplitude control signals;   a high-frequency power switching circuit, having power switching transistors which are selectively switched at a variable duty-cycle, for effecting controlled alternating stator currents;   current sensors, having current transformers with primary windings in series with respective power switching transistors, for providing inductively coupled current feedback pulses proportional to instantaneous current thru the respective transistors;   oscillator means, that provide a high-frequency squarewave signal;   pulse control means, for initiating, from the squarewave signal, staggered pulses each having a restricted duty-cycle, and each having a variable duration dictated by the respective synchronized amplitude control signal and the corresponding current feedback pulse;   switching logic, responsive to the staggered pulses, to said polarities, and to the binary commands, for controlling the selection and duty-cycle of said transistors;   means for sourcing and sinking dc power and high-frequency current.   
     
     
       2. In a controller according to claim 1, a high-frequency power switching circuit, for effecting controlled alternating stator currents; comprising: a power filter capacitor, connected across dc terminals of the dc power source and sink;   four power switching transistors, in a transistor bridge having two ac nodes, a dc node connected to one of said dc terminals, and a dc node connected thru a primary winding of a current transformer to the opposite dc terminal;   four free-wheeling diodes, in a diode bridge having ac nodes connected to respective ac nodes of the transistor bridge and having dc nodes connected across the dc terminals;   an inductor, in series with a stator winding, connected across the ac nodes;   another transistor bridge, diode bridge, and inductor, likewise connected to the dc terminals and to another stator winding.   
     
     
       3. In a controller according to claim 1, a high-frequency power switching circuit, for effecting controlled alternating stator currents; comprising: a power filter capacitor, connected across dc terminals of the dc power source and sink;   two power switching transistors, constituting a first half of a transistor bridge, having an ac node at each end, and a dc node at its center connected to a dc terminal;   another two transistors, each in series with a respective primary winding of a current transformer, constituting a second half of the transistor bridge, having ac nodes connected to respective ac nodes of the first half, and a dc node at its center connected to the opposite dc terminal;   four free-wheeling diodes, in a diode bridge having ac nodes connected to respective ac nodes of the transistor bridge and having dc nodes connected across the dc terminals;   an inductor, in series with a stator winding, connected across the ac nodes;   another transistor bridge, diode bridge, and inductor, likewise connected to the dc terminals and to another stator winding.   
     
     
       4. In a controller according to claim 1, current sensors, for providing inductively coupled current feedback pulses with amplitude proportional to instantaneous current through respective power switching transistors; each comprising: a current transformer, for providing inductively coupled current pulses with amplitude proportional to instantaneous current thru the associated power switching transistors;   a resistive element, connected across the secondary winding of the transformer, with one end at signal ground;   a diode, connected at one end to the secondary winding and at the other end to the current sensor output;   a capacitor, connected at one end to said output and at the other end to the signal ground;   a resistor, in parallel with the capacitor.   
     
     
       5. In a controller according to claim 1, pulse control means, for initiating, from the squarewave signal, staggered pulses each having a restricted duty-cycle, and each having a variable duration dictated by the respective synchronized amplitude control signal and the corresponding current feedback pulse; comprising: first bistable means, for initiating a pulse when set and ending the pulse when reset;   means for setting the first bistable, after a brief delay following each odd transition of the squarewave signal;   means for resetting the first bistable, on the odd transitions;   first comparator means, for resetting the first bistable when a current feedback pulse from a first current sensor overtakes a first synchronized amplitude control signal;   second bistable means, for initiating a pulse when set and ending the pulse when reset;   means for setting the second bistable, after a brief delay following each even transition of the squarewave signal;   means for resetting the second bistable, on the even transitions;   second comparator means, for resetting the second bistable when a current feedback pulse from a second current sensor overtakes a second synchronized amplitude control signal.   
     
     
       6. In a controller according to claim 1, speed sensor means, for deriving from the polyphase transducer signals a continuous analog speed feedback signal proportional to the instantaneous frequency thereof; comprising: means for deriving time-derivatives of each respective sinusoidal transducer signal;   means for squaring the respective time-derivatives;   means for summing the squares;   means for extracting the square-root of the sum.   
     
     
       7. In a controller according to claim 1, a speed sensor circuit, for deriving from the polyphase transducer signals a continuous analog speed feedback proportional to the instantaneous frequency thereof; comprising: first and second op-amp means;   a plurality of like capacitors, each presented a respective transducer signal;   a plurality of diode pairs, each for conducting current from a respective capacitor, during odd half-cycles of the respective transducer signal to the input of the first op-amp, and during the even half-cycles to the input of the second op-amp;   a resistor, across the first op-amp input and output;   a like resistor, one end connected to the first op-amp output, and the other end to the second op-amp input;   a feedback network, across the second op-amp input and output.   
     
     
       8. In a controller according to claim 1, rotation discriminator means, responsive to the polarities of the transducer signals, designated S1 thru S4, for presenting pulses at a first output each indicating a forward-rotation polarity transition, and pulses at a second output each indicating a reverse-rotation polarity transition; comprising: first thru fourth monostable means, for producing a pulse indicating a forward-rotation polarity transition at one of four edge-triggered inputs responsive to S1, S2, S3, and S4, respectively, when an enabling polarity is present at a respective enable input responsive to S4, S3, S1, and S2, respectively;   fifth thru eighth monostable means, for producing a pulse indicating a reverse-rotation polarity transition at one of four edge-triggered inputs responsive to S1, S2, S3, and S4, respectively, when an enabling polarity is present at a respective enable input responsive to S3, S4, S2, and S1, respectively;   logic means for presenting a pulse at the first output each time any of the first thru fourth monostables produces a pulse;   logic means for presenting a pulse at the second output each time any of the fifth thru eighth monostables produces a pulse.   
     
     
       9. In a controller according to claim 1, an absolute value circuit, for deriving the instantaneous magnitude of its input signal; comprising: an op-amp;   first and second diodes, with the input signal presented to the cathode of one and to the anode of the other;   first and second resistors, each of equal resistance, each connected to the negative input of the op-amp, the other end of the first to the first diode, and the other end of the second to the op-amp output;   another resistor, one end connected to the second diode and to the positive input of the op-amp, and the other end to signal ground.   
     
     
       10. In a controller according to claim 1, means for deriving a position feedback analog interpolation signal from the transducer signals; comprising: means for linearizing the magnitude of a transducer signal;   op-amp means, for providing therefrom a zero-centered triangular waveform function of rotor angle;   unity-gain inverting amplifier means, for providing a zero-centered triangular waveform of opposite polarity therefrom;   logic means, responsive to the polarities of each polyphase transducer signal, for providing binary signals therefrom;   analog switch means, responsive to the binary signals, for providing from the triangular waveforms a sawtooth function of rotor angle with transitions that coincide with the polarity transitions.   
     
     
       11. In a controller according to claim 1, signal interface means, for providing signals to control bidirectional rotor speed; comprising: means for producing an analog speed command, proportional to desired rotor speed;   means for producing a negative braking signal, that varies with desired braking torque;   means for producing binary direction commands;   analog combiner means, for providing a speed error signal from the speed command minus the speed feedback;   override means, responsive to the speed error and the braking signal, for providing a torque control signal, which tracks the speed error when the braking signal is zero and when the speed error is the more negative, and tracks the braking signal when it is the more negative;   comparator means, for providing a binary drive command when the torque control signal is positive and a binary brake command when it is negative;   means for deriving a torque amplitue signal, that varies with the absolute value of the torque control signal.   
     
     
       12. In a controller according to claim 1, signal interface means, for providing signals to control rotor speed in compliance with a command pulse rate; comprising: means for providing an analog speed command, proportional to the command pulse rate;   means responsive to the polarities of the transducer signals, for providing a feedback pulse rate proportional to rotor speed;   pulse queuing means, for presenting in addition to each of the feedback pulses each of the command pulses, with a prescribed minimum interval between the queued command and feedback pulses presented therefrom;   up/down counter means, responsive thru the pulse queuing means to the command pulses presented to one input and to the feedback pulses presented to another, for counting the difference thereof;   digital-to-analog converter means, for producing a digitally incremented speed error integral that varies with the accumulated count difference;   signal combiner means, for providing a torque control signal that varies with the analog speed command minus the analog speed feedback plus the speed error integral;   comparator means, for providing a binary drive command when the torque control signal is positive and a binary brake command when it is negative;   means for deriving a torque amplitude signal that varies with the absolute value of the torque control signal.   
     
     
       13. In a controller according to claim 12, feedback and command pulse interpolation means, for synthesizing a linearly variable speed error integral; comprising: means for presenting to the signal combiner a sawtooth function of rotor angle, with peak-to-peak transitions each equivalent to a digital increment and coincident with a feedback pulse;   means for presenting to the signal combiner a sawtooth waveform, with peak-to-peak transitions each equivalent to a digital increment and coincident with a command pulse.   
     
     
       14. In a controller according to claim 12, means for providing the analog speed command, in response to a sawtooth waveform having a constant peak-to-peak amplitude with variable slope intervals between transitions coincident with the command pulses; comprising: a capacitor, to which the sawtooth waveform is presented; an op-amp;   a diode, for conducting current thru the capacitor to the input of the op-amp during the sawtooth slope interval;   another diode, for conducting current thru the capacitor from the signal ground during the sawtooth transition;   a resistor, across the input and output of the op-amp;   a capacitor, in parallel with the resistor.   
     
     
       15. In a controller according to claim 1, signal interface means, for providing signals to control position in compliance with digital commands; comprising: rotation discriminator means, responsive to the polarities of the transducer signals, for providing a feedback pulse at a first output resulting from each forward-rotation polarity transition and at a second output resulting from each reverse-rotation polarity transition;   bistable means, for providing continuous binary direction signals that are updated with each of the pulses;   up/down counter means, that count down due to a pulse at its first input and up due to a pulse at its second input;   means for presenting the feedback pulses from the first and second outputs of the rotation discriminator to the respective first and second counter inputs;   means for sensing a reference position and thereat presetting the counter means to a digital position command;   means for converting the digital output of the counter means to an analog position error signal;   analog switch means, responsive to the analog speed feedback and controlled by the binary direction signals, for providing a velocity feedback signal;   means for providing a torque control signal, which varies with the analog position error signal minus the velocity feedback;   means for deriving a torque amplitude signal, that varies with the absolute value of the torque control signal;   comparator means, for providing a binary forward drive command when the torque control signal is positive and a binary reverse drive command when it is negative.   
     
     
       16. In a controller according to claim 15, pulse-incremented motion control means, for controlling rotation thru an angle dictated by the number of command pulses presented to respective first and second channels, at a variable speed dictated by the command pulse rate; comprising: means for presenting a variable number of command pulses at a variable rate, thru a first channel to effect forward rotation and thru a second to effect reverse;   pulse queuing means, for presenting in addition to each feedback pulse from the first and second outputs of the rotation discriminator to the respective first and second inputs of the up/down counter each pulse from the first channel to the second input and each pulse from the second channel to the first input with a prescribed minimum interval between the queued command and feedback pulses presented therefrom.   
     
     
       17. In a controller according to claim 15, feedback interpolation means, for synthesizing a linearly variable position feedback; comprising: means for combining with the analog position error signal a sawtooth function of rotor angle, with peak-to-peak transitions each equivalent to a digital increment and each coinciding with a feedback pulse.   
     
     
       18. In a controller according to claim 15, interpolated pulse-incremented motion control means, for synthesizing a digital position control servomechanism with linear continuously variable commands and feedback; comprising: means for presenting a variable number of command pulses, at a variable rate thru a first channel to effect forward rotation and thru a second to effect reverse;   pulse queuing means, for presenting in addition to each feedback pulse from the first and second outputs of the rotation discriminator to the respective first and second inputs of the up/down counter each pulse from the first channel to the second input and each pulse from the second channel to the first input with a prescribed minimum interval between the queued command and feedback pulses presented therefrom;   means for combining with the analog position error signal a sawtooth waveform, with peak-to-peak transitions each equivalent to a digital increment and each coinciding with a command pulse;   means for combining with the analog position error signal a sawtooth function of rotor angle, with peak-to-peak transitions each equivalent to a digital increment and each coinciding with a feedback pulse.   
     
     
       19. In a controller according to claim 15, self-programming means, for producing digital readouts to record consecutive positions reached by manual positioning; comprising: means for inhibiting the drive commands;   means for interchanging the first and second inputs to the up/down counter;   reset means, for clearing the up/down counter means to zero prior to departing from each consecutive position;   means for manually rotating the rotor to each consecutive position;   signal lines from the digital output of the up/down counter means, for presenting sequential digital readouts of each consecutive position.   
     
     
       20. In a controller according to claim 15, self-programming means, for producing digital readouts to record consecutive positions reached by pulse-increment positioning control; comprising: pulse-incremented positioning control means, for presenting a variable number of command pulses at a variable rate, from a first channel to the second input of the up/down counter for effecting forward rotation, and from a second channel to the first input for reverse;   means for determining when the servomechanism has reached a reference position and subsequent consecutive positions;   like up/down counter means, that count up with each pulse from the first output of the rotation discriminator and down with each pulse from the second output, for providing sequential digital readouts indicating the direction and amount of rotation from the reference to the first position and from one consecutive position to the next;   reset means, for clearing the like up/down counter means to zero prior to departing from each consecutive position.   
     
     
       21. In a controller according to claim 15, means for limiting slewing speed; comprising: means for providing a reference signal representing maximum desired slewing speed;   means for producing an amplified difference between the reference and the speed feedback when the speed feedback reaches the reference;   signal combiner means, for subtracting the amplified difference from the torque amplitude signal.   
     
     
       22. In a controller according to claim 15, pulse queuing means, for presenting, in addition to each feedback pulse from the first and second outputs of the rotation discriminator to the respective first and second inputs of the up/down counter, each pulse from a first channel to the second input and each pulse from a second channel to the first input, with a prescribed minimum interval between the queued pulses presented therefrom; comprising: first and second channels, for presenting input command pulses;   first and second signal filters, which receive input command pulses from the respective first and second channels, for rejecting interference and presenting filtered pulses;   first and second Schmitt triggers, each respectively responsive to the filtered pulses, for presenting delayed command pulses, each delayed from a respective input command pulse an interval that is less than the pulse duration;   nor-gate means, responsive to the input and the delayed command pulses, for dictating a queuing interval from the leading edge of each input command pulse to the trailing edge of each delayed command pulse;   first and second queuing monostables, for extendably delaying each feedback pulse from respective first and second outputs of the rotation discriminator, with a brief intrinsic delay extended beyond a queuing interval if overlapping therewith;   first and second pulse monostables, responsive to the respective extendably delayed feedback pulses, for presenting queued feedback pulses each having a duration that is less than the delay between the input command pulses and the delayed;   first or-gate means, for presenting the delayed command pulses and the queued feedback pulses from the first Schmitt trigger and second pulse monostable, respectively, to the second input of the counter;   second or-gate means, for presenting the delayed command pulses and the queued feedback pulses from the second Schmitt trigger and first pulse monostable, respectively, to the first input of the counter.   
     
     
       23. In a servomechanism according to claim 1, with the rotor coupled to a magnetically levitated flywheel in a vacuum, signal interface means for providing signals to control power storage and regeneration; including: means for providing a voltage feedback signal proportional to the voltage across the dc power source and sink;   means for providing a dc reference;   means for providing a torque amplitude signal which varies with the difference between the voltage feedback and the dc reference;   means for providing a drive command when the voltage feedback exceeds the dc reference and the speed feedback is below a prescribed level, and for providing a brake command when the voltage feedback is less than the dc reference.   
     
     
       24. Cooperative with a switching controller in a servomechanism for providing regenerative motion control, a polyphase synchronous motor, which provides polyphase transducer signals that each vary sinusoidally with rotor angle in synchronism with the emf of a corresponding stator winding, for producing bidirectional torque proportional to synchronously controlled polyphase stator current and polyphase emf proportional to rotor speed; including in combination: two permanent-magnet rotor end-disks, each providing at one face a pattern of evenly distributed alternating poles from merged looping tangential magnetized paths therein;   permanent-magnet rotor disks, each providing at both faces a like number of evenly distributed alternating poles from axially magnetized paths therethru;   rotatable means for holding a coaxial stack of the rotor disks and end-disks, each affixed to every other with axial spaces therebetween having an aligned axial magnetic field pattern that rotates therewith;   a stator ring, containing polyphase stator windings, and corresponding polyphase transducers which each provide a sinusoidal signal that varies with the axial magnetic field thereat, cemented together in a molded non-ferromagnetic matrix;   stator rings, each containing polyphase stator windings cemented together in a molded non-ferromagnetic matrix;   means for holding a coaxial stack of the stator rings, each fixed to a motor mount, such that corresponding phases are in alignment, and the stator windings and transducers juxtaposed to the rotor disks and end-disks in respective alternation therewith in the axial spaces therebetween.   
     
     
       25. In a motor according to claim 24, a stator ring containing 2-phase stator windings and Hall-effect transducers; comprising: a first winding, constituted by a length of insulated conductor progressively bent between inner and outer concentric arcs of the ring, forming a repeating pattern of unbroken radial and arc segments, the radial segments in groups numbering two less than the rotor poles and having like center-to-center spacing, the arc segments axially offset from the radial by half the axial width, for conducting phase 1 stator current and contributing to phase 1 emf;   a second winding, likewise constituted and formed, for conducting phase 2 stator current and contributing to phase 2 emf;   two linear Hall-effect transducers, with center-to-center spacing half that of the poles, symmetrically disposed within a space reserved from the two windings, for providing 2-phase sinusoidal signals that vary with the axial magnetic field thereat;   a non-ferromagnetic matrix, for containing the two stator windings nested together and the two transducers in respective phase alignment therewith, cemented together and molded into a ring having axially accessible terminations.   
     
     
       26. In a motor according to claim 24, stator rings each containing 2-phase stator windings; comprising: a first winding, constituted by a length of insulated conductor progressively bent between inner and outer concentric arcs of the ring, forming a repeating pattern of unbroken radial and arc segments, the radial segments in evenly spaced groups numbering the same as the number of poles, the arc segments axially offset from the radial by half the total width, for conducting phase 1 stator current and contributing to phase 1 emf;   a second winding, likewise constituted and formed, for conducting phase 2 stator current and contributing to phase 2 emf;   a non-ferromagnetic matrix, for containing the two windings nested together and molded into a ring having axially accessible terminations.   
     
     
       27. In a stator ring according to claim 25, flux-collection means, for concentrating the magnetic field of the rotor thru the transducers and for matching the signal waveform of each transducer with the emf of the corresponding stator winding; each comprising: a ferromagnetic bar having relatively high permeability, its length and breadth approximating that of a radial group of conductors and its width about one-third that of the radial group, in a corresponding angular position to its respective phase and aligned with an adjoining Hall-effect transducer;   a ferromagnetic block having a relatively high permeability, its length and breadth each approximating the breadth of the bar and its width about equal to that of the bar, aligned with and adjoining the opposite side of the Hall-effect transducer.